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Encyclopedia > Homotetrameric

A tetramer is a protein with four subunits (tetrameric). There are homo-tetramers (all subunits are identical) such as glutathione S-transferase, dimers of hetero-dimers such as haemoglobin (a dimer of an alpha/beta dimer), and hetero-tetramers, where each subunit is different. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... In structural biology, a protein subunit or subunit protein is a single protein molecule that assembles (or coassembles) with other protein molecules to form a multimeric or oligomeric protein. ... The Glutathione S-transferase (GST) family of enzymes comprises a long list of cytosolic, mitochondrial, and microsomal proteins which are capable of multiple reactions with a multitude of substrates, both endogenous and xenobiotic. ... 3-dimensional structure of hemoglobin Hemoglobin or haemoglobin is the iron-containing oxygen-transport metalloprotein in the red cells of the blood in mammals and other animals. ... Sucrose, or common table sugar, is composed of glucose and fructose. ... Sucrose, or common table sugar, is composed of glucose and fructose. ...


In Immunology, MHC tetramers can be used to quantitate numbers of antigen-specific T cells (especially CD8+ T cells). MHC tetramers are based on recombinant class I molecules that, through the action of bacterial BirA, have been biotinylated. These molecules are folded with the peptide of interest and β2M and tetramerized by a fluorescently labeled streptavidin. (Streptavidin binds to four biotins per molecule.) This tetramer reagent will specifically label T cells that express T cell receptors that are specific for a given peptide-MHC complex. For example, a Kb/FAPGNYPAL tetramer will specifically bind to Sendai virus specific CTL in a C57BL/6 mouse. Antigen specific responses can be measured as CD8+, tetramer+ T cells as a fraction of all CD8+ lymphocytes.


The reason for using a tetramer, as opposed to a single labeled MHC class I molecule is that the tetrahedral tetramers can bind to three TCRs at once, allowing specific binding in spite of the low (10-6 molar) affinity of the typical class I-peptide-TCR interaction. MHC Class II tetramers can also be made although these are more difficult to work with practically.


 
 

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